The disturbing “suicide challenge” game, which is often spread on WhatsApp, features a viral picture of a woman with huge eyes and a haunting expression.
This avatar sends young people a series of tasks to complete, which become increasingly more graphic and violent, until eventually telling them to kill themselves.
Now one mum has revealed her young son was also exposed to the horror.
The woman, going under the Twitter handle @excusethesasss said: “Parents please pay attention to what your children watch on YouTube!
“I just had my mother ask my three-year-old if he has seen this ‘Momo’ bulls*** and he says yes and that they say they’re going to kill everybody!”
“Parents please pay attention to what your children watch on YouTube!”
Sharing the texts sent by the boy Leo’s grandma, the woman went on: “My child is only three years old! What the f***!”
In the texts, the woman’s mum says: “He said he has heard of Momo and they say they are going to kill everybody.”
She added: “Leo asked does the woman come out of there, meaning from the video?
“I told him, no but if he sees that again ever he’s to let me or you know.”
In a video she shared taken by someone else of a similar Momo Challenge video, the creepy face appears again, accompanied by a child’s voice singing: “Momo is going to kill you”.
It goes on: “Momo comes when you’re in bed. In the morning you will be dead.”
The mum said she would try to email YouTube to stop them from hosting the videos.
In a later text, the grandma went on: “I showed Leo the pic again of that b**ch and I told him they are bad people that are telling kids to do bad thing, I then asked him if they had ever told him to do bad things and he smiled and said yes.”
She said the avatar had told Leo to take drugs and do other bad things.
The disturbing sculpture used in Momo, called Mother Bird, was created in a Japanese special effects company by artist Midori Hayashi, who has no association with the game.
Although many commenters were sympathetic, some argued the woman shouldn’t be letting her three-year-old use YouTube unsupervised at all.
Last week, it was revealed a seven-year-old boy from Manchester had been a victim of the Momo challenge after telling several children at school Momo would kill them in the night.